Refinery operating units are made up of various types of vessels such as tanks, heat exchangers, catalytic reactors, flowlines, distillation towers, desalters, crackers, hydrotreaters and the like. Periodically, these vessels must be cleaned so they can be inspected and maintained to prevent their causing environmental harm and to ensure the continued operational efficacy of the refinery. Cleaning of these vessels typically begins with draining of the vessel of any hydrocarbon being refined which leaves behind oils and sludge which then must be contended with.
Currently, federal environmental laws regulating waste disposal provide incentive for efficient chemical methods for cleaning vessels. Cleaning solutions typically employ ionic surfactants to stabilize oil-in-water emulsions via charge repulsion. These types of surfactants can cause foam and upset the charge balance in downstream water clarification systems. Certain nonionic cleaners employ nonylphenol ethoxylate surfactants which are non-biodegradable and toxic to biotreatment microbes. Other nonionic cleaners use high HLB surfactants (typically 10-20 HLB) which cause foam and require the use of a separate antifoam to prevent foam-overs in open vessels, as well as use of a separate extraction oil to soften heavy hydrocarbons.
Other cleaners use terpene or aromatic type solvents as softeners or extractants for heavy oils. These components can be toxic and/or carcinogenic as well as flammable. They may also mask the odor of other harmful compounds such as benzene. Certain of these cleaners are alkaline or acidic and can be corrosive, while others are oxidizing.